Down-gauging of radiator tube materials puts tough demands on the materials mechanical properties, internal and external corrosion performance, and compatibility between the different components in the radiator when submitted to a brazing operation close to the melting point of aluminium.
Previous attempts have been made to improve the corrosion resistance of brazing sheets by adding Zn and Mg to the coolant side cladding, or waterside cladding. The prior art has been focused on the effect of Mg on the strength and Zn has been added in high amounts to provide the sacrificial anode effect. It has been found that Zn is undesirable in higher amounts since for thinner tube materials, and depending on the brazing operation Zn can diffuse too deep into the core and, as a consequence the corrosion resistance of the whole brazing sheet will be inferior causing pre-stage leakage and failure mode of the end-product.
U.S. Pat. No. 7,387,844 discloses a brazing sheet having a sacrificial cladding material with 2 to 9 weight % of Zn, at least one selected from the group consisting of 0.3 to 1.8 weight % of Mn and 0.04 to 1.2 weight % of Si, and at least one selected from the group consisting of 0.02 to 0.25 weight % of Fe, 0.01 to 0.30 weight % of Cr, 0.005 to 0.15 weight % of Mg, and 0.001 to 0.15 weight % of Cu. This cladding material does not present a sufficient strength and corrosion resistance for thin gauge brazing sheet. It is an object of the present invention to provide a thinner aluminium alloy brazing sheet that has improved strength, and good corrosion resistance on its inner-surface side, which is in contact with a coolant (e.g. water) when being used as a tube or as a header plate for e g heat exchangers, such as in a radiator or heater. It is also an object of the invention to provide a thin brazing sheet material that has a good workability and can be used in situations involving simultaneous severe internal and external corrosive environments, where it significantly enhances the life time by avoiding pre-stage leakage and failure mode from either side